"Over 70% of Californians have received at least one dose. Keep it up, California - get vaccinated," the tweet said.
According to CDC data, California has about 95 new cases over 7 days per 100,000 people. The U.S. as a whole is at nearly three times the rate of California at about 251 new cases over seven days per 100,000 people. Connecticut has the second lowest case rate at 127, and then Colorado is at 128.
"We are not the most vaccinated state," said Dr. Kirsten Bibbins-Domingo, chair of UCSF's Department of Epidemiology and Biostatistics, told the San Francisco Chronicle. "But we are also a state that has not completely abandoned the other mitigation methods."
Masks are required at schools, hospitals and on public transportation, and in counties like Los Angeles, masks are also required indoors.
Montana, Alaska and West Virginia are the worst three states in terms of case rate at 485, 562 and 716 per 100,000 people, respectively.
Within California, CDC data shows the Bay area has the lowest rates: Marin, Santa Clara, Santa Cruz and San Francisco counties all have seven-day total case rates under 80 per 100,000 people. Orange and Ventura counties have rates between about 105 and 115, while Los Angeles, San Bernardino and Riverside counties have rates of 162, 161 and 160 respectively. These are higher than the state's overall rate, but nowhere near the U.S.'s overall rate.
Meantime, South Carolina is setting records for COVID-19 hospitalizations, and new cases are approaching the peak levels of last winter.
Since ending South Carolina's state of emergency on June 7, Republican Gov. Henry McMaster has maintained that parents alone should decide if children wear masks in schools, even as the state's new cases soared from 150 a day on average to more than 5,000.
Now teachers, students and parents are struggling with the fallout as more young people contract the delta variant, forcing nearly two dozen schools and two entire districts back to online learning within a month of returning in person.
State health and education officials say the statewide mask ban in schools took away one of their best tools to stop the spread of COVID-19. The state hit nearly 2,600 COVID-19 patients hospitalized in early September, a record.
"We spiked the football too early. Instead of continuing to listen to medical professionals and interpreting the data, he has been guided by Republican Governors Association talking points," Democratic state Sen. Marlon Kimpson of Charleston said.
Wyoming has one of the highest state rates, with a weekly figure of 659 cases per 100,000 residents, the San Francisco Chronicle reported, and only half of its residents 18 and older are fully vaccinated - trailing every state except West Virginia.
In Arizona, more than 100 daily coronavirus deaths were reported for the second time since February.
The 108 confirmed deaths and 2,742 new coronavirus cases were reported Saturday. Hospitalizations dropped below 2,000 for the first time in nearly three weeks, with 1,981 COVID-19 patients occupying hospital beds on Friday.
That's down from the current surge's high of 2,103 on Sept. 11.
The Associated Press contributed to this report.